For over a century bituminous roofing membranes have been used in the United States to protect buildings, their contents and the occupants from the weather. The most common type of bituminous roofing membranes consist of two to five layers of felts and/or fabrics which, during application to the roof, are made to adhere together with bituminous material such as asphalt, coal, tar, or pitch. The felts and fabrics have contained numerous types of reinforcing materials, such as cellulose organic material, fiberglass, and polyester.
While felts and fabrics have served as well as could reasonably be expected of them, it has generally been recognized that mats consisting solely of polyester would provide substantially superior qualities. For example, polyester exhibits far greater pull-up resistance (i.e., resistance to being pulled or "peeled" away from a surface to which it has been fastened or adhered), and markedly better thermal shock resistance, than conventional fabrics and mats such as felt and fiberglass. It has long been observed that roofing installations subjected to high winds (50 miles per hour or greater) are prone to failure at locations in which sheets have been fastened to roofs by means mechanical fasteners such as nails, which have been used extensively in built-up roofing (BUR) systems. The wind in such situations tends to pull the sheet up away from the roof, causing nail heads to rip through the sheets such that the sheet is completely stripped away from the roof, with consequent loss of water tight integrity. Both inorganic and organic conventional materials have been found to be prone to such failures, whereas polyester, with its superior strength, is greatly resistant to being pulled away. Similarly, polyester has been found to perform much better than conventional materials when subjected to repeated thermal loadings, as by the sun. The constant heating/cooling cycles to which the sun subjects roofs causes continual expansions and contractions in the roof, leading to fatigue failure in sheets and asphalt and to splitting in the membrane itself.
Some success has been seen in using polyester mats installed on-site, by spreading fresh asphalt, applying a layer of polyester, and adding more asphalt on top, but this is time consuming and expensive, and quality control can be exceedingly difficult. A better solution is the use of pre-coated mats, termed "asphalt coated sheets" in the industry. Pre-coated sheets are typically available (in materials other than polyester) in roll form, ready to be laid out and fastened (as by nailing, for example) on a roof or other installation, either as a new membrane or as a re-cap for existing structure. Such a sheet containing polyester would be (and is) a highly-valued product. Thus far, however, no one has been able to reliably, economically, and effectively provide asphalt coated polyester sheets for use in roofing or other waterproofing installations. In order to make such sheets water resistant, and therefore useful, it is necessary to achieve the greatest extent of penetration possible of the asphalt into the mat, which is typically spun woven and therefore not at all air- or water tight on its own. Thus it is generally beneficial to coat the mat with a heated asphalt, which has a reduced viscosity is therefore better suited for penetrating the mat. Hot asphalt has a much lower viscosity than cold asphalt, and is thus much more capable of running down into, or penetrating, the polyester mat. Moreover, it is much easier to control the thickness, uniformity, and quality of an asphalt coating if it is applied while the asphalt is relatively inviscid. But polyester mats, especially those suitable for use in built-up waterproofing installations, typically exhibit relatively high shrinkage rates at even moderately elevated temperatures. Also, it has been observed that polyester mats coated with heated asphalts have experienced excessive shrinkage and wrinkling--so much that until the invention disclosed herein the width and flatness of the finished sheet has been entirely unsatisfactory for standard roofing purposes. This problem is aggravated in attempts to make the mats in conventional roofing line machinery, which is designed to pull strip mat material from rolls through various coating and cooling stages. The tension induced in the mats in such processes increases the tendency of the polyester to stretch in the longitudinal direction (the direction in which the mat is pulled by the machine) and aggravates shrinkage or "necking" in the transverse direction.
Some attempts have been made to use polyester mats in pre-fabricated asphalt coated membranes, but with limited success. One such attempt has involved the use of relatively thick (at least approximately 3/16-1/4") polyester panels to provide heavy membranes through the use of so-called modified bitumen or "mod-bit" processes. Even with the increased thickness of the panels, however, it has been necessary in such processes to move the panels very slowly through the coating line, to apply asphalt to the panel by dipping or pouring (instead of spraying or applying by means of a more economical nozzle), and to immediately cool the panels by immersing them in a water bath in order to avoid distortions such as wrinkling and necking. In addition, relatively large amounts of asphalt are coated onto the panels, so that the finished product is generally at least 1/4" thick. Such thick, heavy panels are extremely unwieldy and inconvenient to package, ship, handle, and install. Thus mod-bit processes are extremely cumbersome, slow, and substantially more complex and expensive than the method disclosed herein. For example, a typical mod-bit line comprising pulling machinery requires the use of a water bath and produces no more than 50 or at the most 100 feet of coated panel per minute.
Thus others interested in superior, economically viable built-up roofing have been forced to turn to the use of other materials, such as fiberglass or organic cellulose or felts for coated built-up roofing products. Some attempts by others in the roofing field to produce an improved roofing material are described in U.S. Pat. Nos. 3,741,856; 3,753,938 and 3,937,640. U.S. Pat. No. 3,741,856 to Hurst issued Jan. 26, 1973, describes a bitumen waterproofing sheet which has a polyethylene support layer and a pressure sensitive adhesive backing. The Montague patent, U.S. Pat. No. 3,753,938, issued Aug. 21, 1973, describes a special roofing material which contains a mixture of bitumen, a synthetic elastomeric material which is predominantly chlorosulphonated polyethylene and fibrous material such as filaments of fiberglass or other synthetic bituminous roofing membrane comprising a base sheet of a synthetic polymer and one or more layers of bitumen. In addition, other roofing membranes have been developed in Europe in an attempt to meet the new requirements of modern roof construction and is the subject of patents in Luxembourg (No. 69480), France (No. 7505703) and Italy (20554A/75). (See also Impermeabilizzazione Delle Construzioni, Romolo Gorgati, 1974 pp. 63-64). The Gorgati patent, U.S. Pat. No. 4,368,228 issued Jan. 11, 1983 describes a bitumen mixture used in a waterproofing membrane obtained by coating different layers of reinforcing materials with the bitumen mixture.
It has also been difficult, for the reasons given above, to produce coated polyester sheets using rubber modified asphalts such as those described in my patent applications Ser. No. 08/978,243, filed Nov. 25, 1997, and entitled "Styrene Ethylene Butylene Styrene (SEBS) Copolymer Rubber Modified Asphalt Mixture"; and Ser. No. 08/978,244, filed Nov. 25, 1997, and entitled "Plasticized Styrene Ethylene Butylene Styrene (SEBS) Copolymer Rubber Modified Asphalt Mixture." Sheets coated with such modified asphalts enjoy all of the advantages offered by those asphalts, including increased resistance to thermal stresses, ozone, and ultraviolet radiation, and may be produced by the methods and apparatus described in this application in the same manner as any other asphalt sheets, without need for modifying the process or apparatus. The specifications for my SEBS modified asphalts are hereby incorporated in this specification, as if set out fully herein, to supplement the processes and explanations provided herein, and to support my teaching of the art of making polyester sheets coated with specially modified asphalts.
It is sometimes advantageous to employ other asphaltic or bituminous mixtures as well, such as for example those modified by inclusion of various organic chemicals or other polymers. In U.S. Pat. No. 5,273,683, issued Dec. 28, 1993 to Dennis Krivohlavek, an exhaustive description of the various prior art approaches to modification of asphalt is presented.
Thus there exists a need for a rollable, lightweight, water-impervious, strong asphalt coated polyester sheet suitable for use in the roofing and waterproofing industries. There also exists a need for a simple, reliable, and cost-effective method for producing such sheets, and in particular for processes for making such sheets at high speed, with simple, economical equipment and without the need for cooling baths.